This is an interdisciplinary Research Project between the departments of Neuroradiology and Neurosurgery at Columbia University. In the previous two years we have built and used experimentally a rotating superconducting magnet for the guidance of magnetic catheters. We have also developed a new intravascular silicon rubber with 1/100th the viscosity of the currently available materials. This new silicon rubber was injected through minute catheters (#2 French) into vascular malformations and tumors in 68 patients. We have also developed a double lumen minute magnetic catheter suitable for intracerebral navigation. We propose to use the magnetic catheter system clinically and develop criteria for a second generation superconducting magnet for catheter guidance. We also propose to further optimize the catheter to obliterate a variety of fistulas and vascular malformations. The use of a new type of balloon will improve guidance.